9.50 The number of cycles to failure for reinforced concrete beams was measured in seawater and in air. The data (in thousands) are as follows:

Seawater: 774, 633, 477, 268, 407, 576, 659, 963, 193 Air: 734, 571, 520, 792, 773, 276, 411, 500, 672 Estimate the difference between mean cycles to failure for seawater and air, using a confidence coefficient of 0.95. Does seawater seem to lessen the number of cycles to failure? (See Hodgkiess et al., Materials Performance, July 1984, pp. 27–29.)